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“Tires are a waste material, and we need to have safe ways to dispose of them,” says Jae Park, a UW professor of environmental engineering. Park's work indicates that ground-up tires provide a safe way to help prevent groundwater contamination.

Park, along with colleagues John Stier and Robert Lisi, studied the absorptive properties of tire rubber for retaining N and P when applied as a distinct subsurface drainage or intermediate layer in golf course putting greens. His results show that a significant reduction in the total concentration of nitrate in leachate was achieved by replacing traditional pea gravel with equally sized granulated tires for the drainage layer media.

“The results indicate that using granulated tires as a drainage layer or fill material beneath sand-based root zones does not compromise the function of the profile or quality of the vegetation while creating an environmentally-beneficial and value-added option for scrap tire reuse,” he says.

Just how the rubber manages to mitigate nitrate pollution remains unclear.

“We don't know exactly how the process of absorption works, but it may result from chemical bonding between the surface of the rubber and the contaminant,” Park says.

Fear that the rubber will eventually become saturated with contaminants doesn't seem to be an issue. The rubber chips, which are typically 2 to 10 cm diameter, are believed to have an unlimited capacity to absorb.

“Sorbed chemicals will be biodegraded by microorganisms after a long acclimation period, regenerating sorption capacity naturally,” Park says.

MAY THE COURSE BE WITH YOU

There are plenty of tires to go around. The Environmental Protection Agency estimates about 242 million tires are discarded every year — one tire for every person in the United States.

Many states have laws preventing old tires from being dumped in landfills. Instead, used tires are collected by the millions in unsightly piles, which compounds the environmental threat because the tires collect rainwater, creating enormous breeding grounds for mosquitoes.

The primary concern of tire piles, though, is the tires' tendency to catch fire, which has not only proven difficult to extinguish but results in the release of harmful gases into the atmosphere.

Tire pile fires can last for weeks, cost millions of dollars to fight, require the evacuation of neighborhoods and cause significant environmental damage from toxic soot fall-out and the run-off of oil from melting rubber.

FREE DROP

Ground-up tires are already used in the soles of sneakers and beneath some football fields, including UW's Camp Randall Stadium.

Park has been working on removal of organic compounds by shredded tires in landfills since 1990 when he found that rubber gasket material can adsorb almost 100 percent of their initial weight when exposed to gasoline, and 40 percent of their initial weight when exposed to mineral spirits.

Park says the idea of applying the concept to golf courses came while he was playing golf with some of his students.

“During the round, we saw a warning sign that pesticides had been recently applied,” Park says. “In passing, I mentioned the advantages of using scrap tires for pesticide removal.”

One student became interested enough to conduct laboratory and field experiments to prove the concept.

“We have also proposed the use of crumb rubber and shredded tires in drainage systems in golf courses,” he says.

Park is currently working on temperature profiles in various rubber layers in an attempt to better understand flora growth periods. Because crumb rubber provides such excellent insulation (shielding the ground from cold and keeping in warm), he postulates that the use of rubber chips may promote better growth during the harsh weather conditions during spring and fall — which could even extend playing periods in the cold weather regions.

“Assuming that the tire material remains inert and does not itself give off toxic by-products, pesticides are not uniform,” Post says.

Pesticides have different structures and degrees of binding to organic matter. They could be expected to have different affinities for the tire material, she says.

The life-span of such a system would also need to be determined, and it would need to be tested under various environmental conditions, such as a high water table or areas with heavy rain and flooding.

An environmental impact report would probably provide answers to these questions and should take place before any implementation occurs. In addition, there should be data supporting the removal of specific pesticides, she says.

Park says he is aware that crumb rubbers cannot remove all pesticides.

“However, crumb rubbers can remove pesticides having solubilities < 10,000 mg/L based on evaluation of molecular structures and polarity,” he says. “We did establish empirical relationships between sorption and octanol-water partition coefficient with crumb rubbers. This allows us to predict the removal efficiency of crumb rubbers for untested organic compounds.”

Scientists cannot test all manmade chemicals so they commonly use this type of approach.

“Most pesticides fit into this range of < 10,000 mg/L, so we believe pesticides can be removed significantly by crumb rubbers,” Park says. “Our paper deals with only nitrate, but I have been working on removal of organic compounds using crumb rubbers for over 15 years.”

Previous research has reported that ground or shredded tires can absorb water contaminants such as benzene, O-xylene and chlorinated hydrocarbons. Park reported in 1996 that tire chips can absorb volatile organic compounds (VOCs) and suggested that tire chips could be used in landfill barriers, soil-bentonite slurry walls, and in wastewater treatment to remove VOCs.

Park said pesticides are removed actually more in the vapor phase than in the aqueous phase; therefore, phase is not an issue.

The reaction rate is relatively fast so that when pesticides dissolved in rain, for example, percolate into crumb rubbers, they are easily sorbed into crumb rubbers, allowing a worst case of less than 10 percent of the pesticides to pass through, he said.

“We are not claiming 100 percent removal,” Park says. “If we can take out most pesticides and let microorganisms biodegrade them, crumb rubbers will maintain relatively effective sorption capacity.”

Park has shown that scrap tires can be granulated to the specifications for the drainage material and applied in putting green construction without hindering traditional performance standards while improving water quality.

“Using crumb rubber as a lighter drainage material or fill has advantages over traditional aggregates in construction of recreational areas such as golf course putting greens and athletic fields on soft foundations as well as potentially reduced labor needs for installation,” he says.

In full-scale tests performed at UW's Turf Grass Research Center, crumb rubber did not introduce adverse effects on turfgrass establishment, density, quality or color, nor was water movement impeded by profiles containing a crumb rubber intermediate or drainage layer compared to a USGA standard putting green.

Right now, Park is hoping to see his idea implemented first on campus, when the university builds a new golf course in the near future.

“When the proposed green construction method is used for an 18-hole golf course, approximately 72,000 tires are required,” he says.

If shredded tires are used as a drainage pipe backfill and embankment material, the number of tires used in golf construction may increase by over 100 percent.

Crumb rubber used as a drainage layer material beneath sand-based root zones may be a value-added reuse of scrap tires.